Focal fatty sparing of the liver
Updates to Article Attributes
Focal fatty sparing of the liver is a localised absence of fatty change in a liver otherwise affected by fatty change (diffuse hepatic steatosis). Recognition of this finding is useful to prevent falsely thinking the region is a mass.
Epidemiology
To be added
Pathology
Similar to its inverse, focal fatty infiltration, regions of focal fatty sparing are thought to have different perfusion characteristics than the rest of the liver. The cause of this is incompletely understood but is thought to result again from alterations in perfusion, either due to compression or invasion of portal venules by the tumour 3.
Radiographic features
Focal fatty sparing typically has a geographic appearance and occurs in characteristic locations 1,3:
- adjacent to the porta hepatis (segment IV)
- gallbladder fossa
- adjacent to the falciform ligament
- subcapsular parenchyma
Important features, along with location and echogenicity/density/intensity are 2:
- absence of mass effect
- absence of distortion of vessels that run through the region
When it occurs outside of these areas or has a nodular appearance, it may become problematic distinguishing it from a focal liver lesion, especially as regions of focal sparing may be seen around focal liver lesions 2,3.
Ultrasound
Liver with fatty change demonstrates increased echogenicity and attenuation 2. The echogenic walls of the portal veins and hepatic veins are lost, due to the increased liver echogenicity.
CT
Affected regions demonstrate reduced liver attenuation on both precontrast and portal venous phase imaging. It is important to remember that the spleen enhances earlier than the liver (due to systemic arterial supply rather than predominantly portal) and thus arterial phase or very early portal venous phase scans should not be used.
MRI
Requires both in- and out-of-phase imaging and contrast to adequately assess 1.
Pseudolesions (focal sparing) are better seen on out-of-phase imaging, but otherwise appear normal and similar to the rest of the liver on T2 and contrast-enhanced sequences 1.
The rest of the liver demonstrates:
- T1: hyperintense
- T2: mildly hyperintense
- IP/OP: signal drop out in out-of-phase
Treatment and prognosis
When focal sparing is idiopathic, and not related to a hepatic focal mass, then the prognosis is that of a patient with diffuse hepatic steatosis.
Differential diagnosis
See also
-</ul><p>When it occurs outside of these areas or has a nodular appearance, it may become problematic distinguishing it from a focal liver lesion, especially as regions of focal sparing may be seen around focal liver lesions <sup>2,3</sup>. </p><h5>Ultrasound</h5><p>Liver with fatty change demonstrates increased echogenicity and attenuation <sup>2</sup>. The echogenic walls of the portal veins and hepatic veins are lost, due to the increased liver echogenicity.</p><h5>CT</h5><p>Affected regions demonstrate reduced liver attenuation on both precontrast and portal venous phase imaging. It is important to remember that the spleen enhances earlier than the liver (due to systemic arterial supply rather than predominantly portal) and thus arterial phase or very early portal venous phase scans should not be used.</p><h5>MRI</h5><p>Requires both in- and out-of-phase imaging and contrast to adequately assess <sup>1</sup>.</p><p>Pseudolesions (focal sparing) are better seen on out-of-phase imaging, but otherwise appear normal and similar to the rest of the liver on T2 and contrast-enhanced sequences <sup>1</sup>. </p><p>The rest of the liver demonstrates:</p><ul>- +</ul><p>When it occurs outside of these areas or has a nodular appearance, it may become problematic distinguishing it from a focal liver lesion, especially as regions of focal sparing may be seen around focal liver lesions <sup>2,3</sup>. </p><h5>Ultrasound</h5><p>Liver with fatty change demonstrates increased echogenicity and attenuation <sup>2</sup>. The echogenic walls of the portal veins are lost, due to the increased liver echogenicity.</p><h5>CT</h5><p>Affected regions demonstrate reduced liver attenuation on both precontrast and portal venous phase imaging. It is important to remember that the spleen enhances earlier than the liver (due to systemic arterial supply rather than predominantly portal) and thus arterial phase or very early portal venous phase scans should not be used.</p><h5>MRI</h5><p>Requires both in- and out-of-phase imaging and contrast to adequately assess <sup>1</sup>.</p><p>Pseudolesions (focal sparing) are better seen on out-of-phase imaging, but otherwise appear normal and similar to the rest of the liver on T2 and contrast-enhanced sequences <sup>1</sup>. </p><p>The rest of the liver demonstrates:</p><ul>
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